Using cutting-edge technologies including next-generation sequencing of laser capture microdissected tissue, we are comparing the mutation profile of tumor samples to cell-free DNA purified from matched plasma. Using a series of carefully generated spike-in controls, we are testing the limits of sensitivity and specificity for quantifying point mutations from sequenced ctDNA libraries and determining the relationship between the sequencing result and starting material. We have further performed ultra-low pass whole genome sequencing on the plasma from 200 patients in an effort to prioritize allele-specific detection in those patients with the greatest volume of ctDNA.